1. Field of the Invention
The present invention relates to a magnetic recording and playback apparatus, particularly a magnetic recording and playback apparatus for controlling recording by sensor input in a monitoring video tape recorder mainly intended for prevention of crimes.
2. Description of the Background Art
An apparatus named sensor VTR or long-hour VTR has already been put to practical use as monitoring VTR mainly intended for prevention of crimes.
Explanation will be given hereafter on the construction and actions of conventional sensor VTR and long-hour VTR by using FIG. 7. FIG. 7 is a block diagram showing the construction and actions of sensor VTR and long-hour VTR. In FIG. 7, a video camera 201 is connected to a video signal amplifier 1 through a video signal input terminal 203. The video signal amplifier 1 is connected with a video signal recording device 2 for modulating video signals, the video signal recording device 2 may be into FM signals an FM modulator. The video signal recording device 2 is connected with an FM signal amplifier 3 for amplifying FM signals and recording them on magnetic tape by passing recording current to the video head.
The FM signal amplifier 3 is connected in such a way that its output signals may be given to video heads VL and VR incorporated in a rotary drum 100 through an I/O selecting switch 4 for switching input and output of the video heads in both recording mode and playback mode.
Moreover, the video heads VL and VR are connected in such a way that their output signals may be given to a video signal playback device 5 which may include an FM demodulator, through the I/O selecting switch 4. The video signal playback device 5 is connected to a video output terminal OUT.
The rotary drum 100 gets in contact with a magnetic tape 101 while turning, and the magnetic tape 101 is conveyed by being pinched between rotating capstan shaft 102 and pinch roller 103. Moreover, the capstan shaft 102 rotates by receiving the rotation of a non-illustrated capstan motor which is connected to a capstan motor driving device 6.
Here, the video signal amplifier 1, video signal recording device 2, FM signal amplifier 3, I/O selecting switch 4, video signal playback device 5 and capstan motor driving device 6 are connected to a system controller 7 and controlled by control signals from the system controller 7. The system controller 7 is a device for outputting control signals by receiving signals from a sensor i.e. a door switch 202 which is attached to a door and closes its contact when the door is opened, for example.
Next, explanation will be given on actions. First, explanation will be given on actions in the case where said construction is used as a sensor VTR which acts in linkage with a sensor. In FIG. 7, the contact of the door switch 202 remains open (hereinafter referred to as "OFF") while the door is closed.
At this time, the system controller 7 maintains the state of standby for recording by detecting that the door switch 202 is OFF. In this state of standby for recording, at least the system controller 7 is working and is constantly detecting the open/close state of the contact of the door switch 202.
In the state of standby for recording, there is no need of working of the video signal amplifier 1, video signal recording device 2 and FM signal amplifier 3, but there are also cases where those devices are put in a state ready for immediate passage to recording state from the state of standby for recording. However, the capstan motor driving device 6 is at stop, the magnetic tape 101 is not conveyed and the image of the video camera 201 is not recorded on the magnetic tape 101.
Here, if someone invades the room by opening the door, the door switch 202 closes (hereinafter referred to as "ON"), and the system controller 7 detects it and starts recording by activating the video signal amplifier 1, video signal recording device 2, FM signal amplifier 3, I/O selecting switch 4, video signal playback device 5 and the capstan motor driving device 6.
The system controller 7 is provided with a timer switch which is not shown in the drawing and is capable of setting the duration of maintenance of recording state after start of recording by setting the recording time in advance by means of this timer switch. Therefore, even if the door is closed immediately after opening, the sensor VTR maintains the recording state until the set time elapses. When the time set by the timer switch has elapsed, the system controller 7 will switch the respective devices to the state of standby for recording again and maintain the state of standby for recording until the door is opened next time. This will make it possible to record the behaviors of anyone who breaks into the room on the magnetic tape 101 during the time set on the timer switch from the point in time when the door is opened.
Next, explanation will be given on actions in the case where said construction is used as a long-play VTR which performs recording over a long period of time. In FIG. 7, the system controller 7 maintains the state of intermittent recording by detecting that the door switch 202 is OFF when the door is closed. In this state of intermittent recording, the system controller 7, video signal amplifier 1, video signal recording device 2 and the FM signal amplifier 3 are working in the recording state. The capstan motor driving device 6 controls the capstan motor in a way to repeat sequential actions of drive.fwdarw.stop.fwdarw.drive.fwdarw.stop. As a result, the magnetic tape 101 is carried intermittently and fragmentary video signals which are discontinuous in time are recorded on the magnetic tape 101. (Hereinafter, the method of recording fragmentary video signals which are discontinuous in time will be designated as "intermittent recording" and the method of continuously recording video signals will be designated as "continuous recording.) Intermittent recording has an advantage of possibility of making a long-hour recording on a single tape.
If, in this state, someone breaks into the room by opening the door, the door switch 202 is turned ON and the system controller 7 detects it and switches the capstan motor driving device 6 to a state of continuous recording. In the state of continuous recording, the capstan motor turns at a constant speed and the magnetic tape 101 is conveyed at a constant speed, making it possible to record video signals which are continuous in time on the magnetic tape. The system controller 7 is provided with a timer switch which is not shown in the drawing and is capable of setting the duration of maintenance of recording state after start of recording by setting the recording time in advance by means of this timer switch. Therefore, even if the door is closed immediately after opening, the long-play VTR maintains the state of continuous recording until the set time elapses and, when the set time has elapsed, the system controller 7 will switch the capstan motor driving device 6 to the state of intermittent recording again and maintain the state of intermittent recording until the door is opened next time. This will make it possible to record the behaviors of anyone who breaks into the room during the time set on the timer switch from the point in time when the door is opened.
As explained above, a conventional sensor VTR recorded images after the point in time when it obtained signals from a sensor represented by a door switch 202 provided on the door. Moreover, a long-play VTR made continuous recording from the point in time when it obtained signals from a sensor but recorded only fragmentary video information which is discontinuous in time about video signals produced before the sensor starts working.
Therefore, the conventional sensor VTR and long-play VTR do not continuously record in detail the situation from before the start of working of the sensor, to know how the invader opened the locked door, for example.